Speed control of d. c. motors.



H. V. GREEN.

SPEED CONTROL OF D. C. MOTORS.

APPLICATION FILED MAY 27. 1914.

1 ,1 90, 1 50. Patented July 4, 1916.

Fig. l v

1! l i I l Wins/E5555 ZIVVENTUR W HARULU VEREEN v j 42w MM 1505A?"TURNEY UNITED STATES, PATENT onrrcn' HAROLD V. GREEN, OF CHICAGO,ILLINOIS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEWYORK.

T all'whom it may concern:

Be it known that I, HAROLD V. GREEN, a citizen of the United States,residing at Chicago, in the county of Cook, State of Illinois, haveinvented certain new and useful Improvements in Speed Control of D. C.Motors, of which the following fication.

My invention relates to the speed control lo of direct current motorsand more especially to the adaptation of a vibratory regulator of theTirrill type to this purpose.

It is well known that'the speed of a direct current motor may the fieldexcitation, as by means of a res1stance in series with the shunt fieldwinding of the motor. For constant speed, this resistance may becontrolled by an electrically operated switch arranged to insert andremove the same from the field circuit, the resultant effect beingdetermined by the relative length of time during which the resistance'isleft in circuit. Such an arrange: ment is shown in the U. S'. patents toStebbins, #84 9,582,- and Tirrill, #1,029,480, and in each of thesepatentsthe coil operating the switch is energized from a generatordriven by the motor. however, there must be an actual change of speedbefore the regulator can be set in ope- 'eration, and the result will bea fluctuation of speed above and below desired. This fluctuation orhunting is undesirable, since it may readily be cumulative and produce aconsiderable speed variation.

The object of my invention is to devise a regulator which shall holdthe. speed of a direct current motor constant at any de- 40 sired va1ue.r 7 Another object is to provide a regulator -which shall be responsiveto tendencies toward change of speed of the motor and hold actualconstant speed at any load, and independent of voltage fluctuations inthe sup p X further object is to make the regulator accuratelyresponsive to sudden variations of motor .armature current and at thesame time to provide for compensation for changes in load. v Stillanother object is to provide convenient means for adjusting"theregulator sothat it will hold constant speed at any desired point in thespeed range ofthemotor,

Specification of Letters Patent.

the Tirrill is a specibe controlled by varying With such devices,

the exact speed Patented July 4, 1916.

Application filed May 27, 1914. Serial No. 841,199.

According to my invention, a regulator of which short-circuits aresistance in the shunt field circuit of the motor.

. Preferably, the regulator will have two floating contacts, althoughthis is not essential, and the solenoid coil controlling one of thesecontacts will be supplied with a current proportional to the armaturecurrent by being connected in shunt with an inductive resistance whichis in series with the type is used to control a relay motor. Thesolenoid coil controllingthe other contact will be supplied with currenti from a generator driven by the motor. Opposing this coil I alsoprovide a compensating 'coil supplied with a current propor tionalto themotor armature or load current.

For convenience in adjusting the regulator to correspond with differentspeed settings of the motor, I provlde two rheostats, simuL taneouslyadjustable, one in the shunt field circuit of the motor and the other inthe circuit of the coil supplied by the generator. y invention willbebest understood by reference to the accompanying drawing, in whichFigure 1 is a diagrammatic view showing one arrangement of the apparatusinvolved, and Fig. 2 is a view showing another arrangement of certain ofthe parts.

The motor 1', whose speed is to be regulated, is supplied with .current'from the mains 2, and as shown is'constructed with both a series field 3and a shunt field 4. Oleviously, however, the series field is notessential. Driven by the motor, and here shown as mounted on the sameshaft, is a pilot generator 5. This generator may be of any size ortype, but if its use is solely for,the purpose of regulation, it ispreferably of the magneto type and of small size. A regulator 10, whosearrangement constitutes the object of my invention, is here shown as ofthe Tirrill type employing two floating contacts controlled bysolenoids. As will later appear, such a construction is not absolutelyessential for speed regulation, and the regulator will operate to holdapproximately constantspeed if one of the contacts remains in a fixedposition.

In the form shown, a pivoted contact arm 11 is controlledby asolenoid 12and a spring 13. The other contact arm 14 is controlled In order thatthe movement of this contact may be smooth and gradual, I provide adash-pot-18 of ordinary construction oper- 21. The solenoid 12 isconnected in shunt of say 1,000

withv the resistance 20, while the solenoid 16 is connected in shuntwith the resistance 21. Preferably, the solenoid winding 16 is providedwith taps and a switch 19 arranged to vary the number of operative turnsthereof. The solenoid 15 is supplied with current from the generator 5.

Controlled by the floating contacts of the regulator 10 is a relay 30acting upon a spring-held armature 31 arranged to shortcircuit aresistance 32 in the shunt field circuit of the motor. Preferably, acondenser 33'is connected across the contacts of this relay, whichprevents sparking. In circuit with the shunt field of the motor is arheostat 40, and in circuit between the solenoid coil 15 and thegenerator 5 is an adjustable rheostat 41. The movable arms of theserheostats are operatively connected in any desired manner, as by theshaft 42 here shown. In practice it will be found desirable to designthe rheostat 40 with resistances of such value that the various stepswill give equal increments of speed variation of the motor, while therheostat 41 will be designed with steps having equal resistances.

Another arrangement is shown in Fig. 2, where in place of the tworesistance shunts 20 and 21 in the mains 2, I use simply an induotiveresistance 20 and connect the solenoid coils 12 and 16 in series acrossthis shunt. Otherwise, the arrangement is the same as in Fig. 1.

The various elements going to make up the arrangement illustrated areall well known of themselves, and, accordingly, the diagrammatic showingand the preceding description are believed to be suflicient to enableany one skilled in the art to utilize the invention. The objects of myinvention, however, will be more readily understood by considering theoperation of the particular arrangement of the apparatus hereinillustrated.

Let us suppose that the motor is running at some s eed. say 900 R. P. M.Now, if we hold the oating contacts apart the relay 30 will bedeener'gized, and, consequently, the regulator will have no effect uponthe speed, since the resistance 32 will be constantly short-circuited.If, now, we force the floating contacts together and hold them thus, therelay 30 will attract the armature '31 and remove the short-circuitaround the resistance 32, thereby decreasing the field excitation,whereupc n the motor will reach a speed P. M. Let us now release thecontact arm 14, still holding the contact arm 11 in a fixed position. Ifthe rheostats 40 and 41 have been set to hold the motor at 050 R. P. M.,then the excess voltage of the pilot generator 5 will raise the plungerwithin the solenoid 15 and open the floating contacts, therebystrengthening the motor field. The speed will then diminish to a valueslightlybelow 950 R.. 1. M., at which point the voltage of the pilotgenerator will have fallen to such a value that the floating contactswill close and the motor field weaken, thus causing an increase in thespeed of the motor. The operation described will now be repeated, andthe speed of the motor will fluctuate up and down above and below 950It. P. M., in an attempt to hold constant voltage on the pilotgenerator. Thus, it can be seen that approximate speed regulation isobtained as described in the patents previously referred to, but thatactual speed regulation cannot be obtained without actual speedvariation, which in itself will give a tendency to hunting. Now, let ushold the contact lever 14 in a fixed position, and allow the lever 11 tovibrate. If the floating contacts close, the field current of the motorwill weaken, which will tend to increase the speed of the motor.However, assuming constant line voltage and constant load, the in--crease in speed of the motor is only possible by means of an increase inthe armature current. Such an increase in the annature current willresult in pulling down the core within the solenoid 12, thereby openingthe floating contacts. This will strengthen the field of the motor,which will tend to decrease its speed and decrease the the previousoperation will be repeated.

Since the lever 14 with its attached spring and solenoid core will havebut a small moment of inertia, it will be in a state of practicallyconstant vibrationand' the resultant effect will be determined by therelative proportion of the time durin which the contacts are opened andclose From this description, however, we see that the regulator willoperate even if the contact attached to the lower arm 14 is held infixed position, and that the result will be the regulation of the motorspeed, even though there is no change in the voltage of the pilotgenerator, which is the same as saying that there is no change in thespeed of the motor. We have, therefore, attained one of the objects ofthe invention, viz: good regulation without speed variation.

It is now desirable to consider the operation of the regulator withchanges in load on the motor. If the motor is operating at no load andat a definite speed and full load is suddenly thrown on, there will be apermanent increase in the current sup-plied to the motorarmature, andhence in the pull exerted by the solenoid l2. The effect of crease inmotor speed would mean an in crease in the voltage of the pilotgenerator 5,

and hence an effort to hold the floating contacts still farther apart.In order to avoid this undesirable result, I have provided acompensating coil 16 which opposes the sole noid coil 15 and with anincrease in load tends to raise the contact carried by the lever arm 14adjacent to the-contact of the lever arm 11. By the proper design of thecoil 16, exact compensation for changesin load may be eifected'so thatthe regulator will operate groperly to hold constant speed at all loads.

y adjustment of the switch 19 and the operative turns in the coil 16, itis possible to adjust the regulator so that the speed of; the motor willincrease with increasing load, that is to say, over-compensation; ordecrease with increasing load, that is to say, under-compensation.

In order that the sudden fluctuations of armature current produced bythe rapid opening andclosing of the regular contacts may-have a propereffect on the rapidly vibrating lever arm 11, Ihave shown the shunt 20,around which the solenoid 12 is connected, as an inductive shunt, sothat the proper I proportions of the rapidly fluctuating 'arma turecurrent will-be forced to pass through this coil and not be kept out bythe inductance thereof. Since the core wlthin the coil 16 is connectedwithin the dash-pot 18, its movements are necessarily gradual, and suchan arrangement is not necessary. Preferably, therefore, a separatenon-inductive shunt will be provided, as shown in Fig. 1; but, ifdesired, the coils 12 and 16 may be connected in series across a commoninductive shunt, as illustrated-in Fig. 2.

Fluctuations in the voltage of thesupply mains would ordinarily causevariations in the motor speed; but with the regular operating as'hereinshown, an increase in voltage would first'be made manifest by anincrease in the armature-current. This would,

however, act upon the solenoid 12 to open the floating contacts, andthereby-increase 'the motor .field and-decrease its speed. A

reverse 'operation'would occur upon a decrease in voltage; Thus, we seethat theregulator is able to anticipate and control the eifects'ofexternal voltage fluctuations. With the pparatus arranged to holdconstant speed at any particular point, the cur-- rent in the coil 15,supplied from the pilot generator 5, is practically constant, and themovement of the lever 14 is slight and the changes-gradual, due to thedash-pot 18. If, now, it is desired to adjust the apparatus to holdconstant speed at another value by adjustment of the rheostat 40, itwill only be necessary at the same time to adjust the rheostat 41 andincrease the resistance in the circuit supplied by the pilot generator5. This will mean that in order to-maintain the same current in the coil15 there must be an increase in the voltage of the pilot generator; or,in other words, there must be a definite increase in the speed of themotor for each step on the rheostats 40 and 41. Obviously, the movementof the rheostat arms will give an indication of the speed at which weare to, hold the motor constant.

Thus, it will be seen that I have provided an arrangement whereby thespeed may be held constant at any desired value, and that it is adaptedfor variable speed drive for paper-making machines.

Obviously, the arrangement may be equally well applied to numerous otheruses, and various changes and modifications in the particulararrangement shown and described may be made. 'I, accordingly, do notdesire to be limited to the precise arrangement shown, but seek to coverin the appended claims those modifications and combinations which fallproperly within the true scope and spirit of my invention.

What I claim as new and desire to secure 1. In combination, a directcurrent motor provided with a shunt field winding, a resistance inseries with said field winding, a relay for short-circuiting saidresistance, an inductive resistance in series with said motor, asolenoid operated contacter controlling said relay and connected inshunt with said inductive resistance to hold said motor at constantspeed.

2. In combination, a direct current motor provided with a shunt fieldwinding, a generator driven by said motor, a resistance in series withsaid motor field winding, a relay for short-circuiting said resistance,floating contacts controlling said relay, a solenoid, controlling one'ofsaid contacts, supplied with a current proportional to the motorarmature current, and another solenoid, controlling the other contact,supplied with current by said generator.

3. In combination, a direct current motor provided with a shunt'fieldwinding, a gen-' erator driven by said motor, a resistance in serieswith said motor field winding, a relay for shortcircuiting saidresistance, floating contacts controlling said relay, a solenoid,controlling one of said contacts, supplied with a current proportionalto the motor.

contacts controlling said relay, an inductive resistance in series withsaid motor, a solenoid controlling one of said contacts connected inshunt with said inductive resist-' ance, another solenoid controllingthe other contact electrically connected to said generator, anon-inductive resistance in series with said motor, and a third solenoidopposing the second mentioned solenoid and connected in shunt with saidnon-inductive resistance.

5. In combination a direct current motor provided with a shunt fieldwinding, a generator driven by said motor, a resistance in series withsaid motor field winding, a relay for short-circuiting said resistance,floating contacts controlling said relay. an inductive [BELL]Corrections in Letters Patent No; 1,190,150.

resistance in series with said motor, a solenoid controlling one of saidcontacts connected in shunt with said inductive resistance, anothersolenoid controlling the other contact electrically connected to saidgenerator, and a third solenoid opposing the second mentioned solenoidand responsive to the motor armature current.

6. In combination, a direct current motor provided with a shunt fieldwinding, a direct current generator driven by said motor, an adjustableresistance in series with said motor field winding, a relay forshort-circuiting a portion of said resistance, floating contactscontrolling said relay, a solenoid, controlling one of said contacts.supplied with a current proportional to the motor armature current,another solenoid, controlling the other contact, supplied with currentfrom said generator, an adjustable resistance in circuit with the lastnamed solenoid, and means for simultaneously adjusting said resistances.

In witness whereof, I have hereunto set my hand this 20 day of May 1914.

HAROLD V. GREEN.

It is hereby certified that in Letters Patent No. 1,190,150, grantedJuly 4, 1916, upon the application of Harold V. Green, of Chicago,Illinois, for an improvement in Speed Control of D. C. Motors,

requiring correction as follows: Page 2, line 1, for the word movementread "errors appear in the printed specification movements; same page,line 118, for the Word lower read lever; line 125, for the word goodread speed; page 3, lines 33 and 52, for the word regular readregulator; and that the said Letters Patent should be read with thesecorrections therein that the same may conform to the record of thecasein the Patent Ofiice, Signed and sealed this 22d day of August, A.D., 1916. i

I F. W. H. CLAY, Acting Omnmiasioner of Patents.

